1. Technical Field
The present invention relates to air conditioning systems that utilize refrigerants and a compressor, and particularly to air conditioning systems capable of effectively alleviating excessive increases in refrigerant discharge pressure within a heating circuit.
2. Description of the Related Art
A known air conditioning system is disclosed in Japanese Patent Application No. 7-19630 and includes a compressor 1, a cooling circuit 51, a heating circuit 52 and a controller 83, as shown in FIG. 1.
The cooling circuit 51 includes a condenser 55, a first expansion valve 57, and a heat exchanger 59 provided on a passage connecting a discharge port D to a suction port S of the compressor 1. High-pressure refrigerant discharged from the discharge port of the compressor 1 is drawn through the above respective devices and back to the compressor 1.
The heating circuit 52 includes a bypass passage 52a that extends from the discharge port D of the compressor 1 to the heat exchanger 59. A second expansion valve 63 is provided within the bypass passage 52a between the discharge port D and the heat exchanger 59. The high pressure refrigerant discharged from the compressor 1 is not directed to the condenser 55, but rather is drawn by the compressor 1 through the second expansion valve 63 and the heat exchanger 59 and this cycle is repeated. Such a heating circuit 52 is generally known as a hot-gas bypass heater.
The operation of the cooling circuit 51 and the heating circuit 52 is changeably selected by opening and closing selector valves 53a and 53b, which opening and closing operations are performed by the controller 83.
Because the air conditioning system is used in a state in which the refrigerant discharge pressure is higher when the heating circuit 52 is used than when the cooling circuit 51 is used, abnormally high pressure is likely to be applied during operation of the heating circuit 52. For example, the abnormally high-pressure state is likely to occur when a rotation speed of the compressor 1 is increased temporarily during operation of the heating circuit 52. Therefore, the air conditioning system is further provided with a refrigerant releasing passage 91 having a pressure relief valve 93. The refrigerant releasing passage 91 is connected to the heating circuit 52 and the cooling circuit 51 and the pressure relief valve 93 can be opened to release the refrigerant from the heating circuit 52 to the cooling circuit 51 when the refrigerant discharge pressure abnormally increases during the operation of the heating circuit 52.
Because the cooling circuit 51 and the heating circuit 52 are alternatively selected by the selector valves 53a and 53b, the refrigerant is released toward the cooling circuit 51 which is not used when the discharge pressure is increased abnormally during operation of the heating circuit 52, thereby preventing the discharge pressure at the heating circuit 52 from increasing abnormally.
Because the refrigerant is released from the operating heating circuit 52 to the cooling circuit 51 which is not used, the abnormally high-pressure state of the discharge pressure during operation of the heating circuit 52 can be alleviated. However, because the refrigerant in the heating circuit 52 is released into the cooling circuit 51 whenever the discharge pressure increases, the amount of the refrigerant in the heating circuit 52 is reduced and heating performance may be reduced. Moreover, because the high-pressure refrigerant is wastefully released from the heating circuit by working the compressor 1, energy efficiency is reduced.
It is, therefore, an object of the present invention to provide an air conditioning system that can effectively alleviate abnormally high pressure state.
Preferably, the air conditioning system may include a compressor, a heating circuit, and a capacity controller. The compressor has a suction port, a discharge port, a driving unit provided within a compressor driving chamber, a first passage and a second passage. The driving unit may decrease compressor output discharge capacity when the pressure within the driving chamber increases. The first passage may connect the discharge port to the driving chamber and the second passage may connect the driving chamber to the suction port. The capacity controller may open the first passage when the refrigerant discharge pressure reaches or exceeds a high set point pressure, that is, a predetermined pressure. By opening the first passage, the high-pressure refrigerant may be released from the discharge port to the driving chamber through the first passage. Thus, the pressure within the driving chamber may increase. By increasing the pressure within the driving chamber, the compressor output discharge capacity can be reduced. As the result, the discharge pressure of the compressor will be reduced by the reduction in the compressor output discharge capacity.
In particular, the air conditioning system can solve a problem of insufficient heating performance due to release of the refrigerant within the heating circuit into the cooling circuit for alleviating the abnormally high-pressure state of the discharge pressure during operation of the heating circuit. Moreover, the air conditioner can solve a problem of low energy efficiency due to wasteful release of the high-pressure refrigerant from the heating circuit to the outside.
As another example, the air conditioning system may preferably include a capacity controller that can close the second passage, when the refrigerant discharge pressure reaches or exceeds a high set point pressure, that is, a predetermined pressure. In this example, the high-pressure refrigerant may be released at all times from the discharge port to the driving chamber through the first passage. The refrigerant within the driving chamber may be released into the suction port through the second passage in a normal operation of the air conditioning system. By releasing the refrigerant from the driving chamber into the suction port, pressure within the driving chamber can not increase in a normal operation. To the contrary, the capacity controller can close the second passage when the discharge pressure reaches or exceeds a high set point pressure, that is, a predetermined pressure. By closing the second passage, refrigerant can not be released from the driving chamber into the suction port through the second passage. Thus, the pressure within the driving chamber may increase. By increasing the pressure within the driving chamber, the compressor discharge capacity can be reduced. As the result, the discharge pressure of the compressor can be reduced by the reduction in the compressor output discharge capacity.